Backflow prevention apparatus



`Fan. 16, 1951 Filed Feb. 16, 1944 l.. l.. SNYDER 538,281

BACKFLOW PEVENTION APPARATUS 2 Sheets-Sheet l Jan. 16, 1951 L. sNYDER2,538,281

BACKF'LOW PREVENTION APPARATUS Filed Feb. 1e, 1944 2 sheets-sheet 2Patented Jan. 16, 1951 BACKFLOW PREVENTION APPARATUS Leonard L. Snyder,Montebello, Calif.

Application February 16, 1944, Serial N o. 522,575

9 Claims.

This invention relates to apparatus employed for establishing aunidirectional now of liquid from a supply source to a point of use andwherein means are provided for preventing reverse flow.

One of the objects of the present invention is to provide apparatus ofthis character in which a regulator valve is mechanically controlled asdifferentiated from hydraulic control.

Another object of this invention isV to provide a unidirectional flowsystem in which there is incorporated a mechanically operateddifferential regulated valve operative to maintain a pressuredifferential between the Supply pressure and the consumers pressureduring normal iiow and at cessation of normal flow.

Another object of the invention is to provide improved means forcontrolling a drain valve, which can be relied upon to effect automaticopening of this valve if the differential pressure referred to fallsbelow a predetermined minimum.

Another object of this invention is to provide in such a supply system adrain valve which will open and remain open as long as the supplypressure is below or slightly above atmospheric pressure.

hereinafter.

The invention consists in the novel parts and combinations of parts tobe described hereinafter, all of which contribute to produce aneiiicient back now prevention apparatus.

In the drawing:

Fig. l is an elevation partially in section of apparatus embodying thisinvention, and illustrating a pilot-valve control device cooperatingwith the other parts of the apparatus to control the drain valve andeffect its automatic opening under conditions where a reversal of thenormal direction of flow in the pipe line is imminent or occurring.

Fig. 2 is a view similar to Fig. l, but illustrating this controlapparatus with the pilot-valve control eliminated, so that the controlapparatus actuates the drain valve directly.

Fig. 3 is a side elevation and partial section illustrating anotherembodiment of the invention, and in which the drain valve and regulatorvalve are installed in a casing in which the pressurecontrolled chamberis formed and located between the supply line and the consumers line.

Referring to Fig. l, I indicates the supply line and 2 indicates theconsumers line between which a duct or pipe connection 3 is provided,through which the` liquid, such as water, passes,

Further objects of the invention will appear the normal direction ofiiow being from left to right as indicated by the arrow.

Between the supply line l and the intermediatev duct or connection 3, Iprovide a iiow control valve 4 which is of poppet type; that is to say,the casing of the valve 4 carries a valve closure 5 that is urged towardits seat 6 through the agency of a coil spring l. The valve closure 5 iscentered and guided through the agency of a valve stem 8 that extendsupwardly and is guided in a guide bore 9 formed in the cap i of thevalve that screws down onto its body. The underside of the Valve closure5 is provided with guide wingsA Il that maintain the valve closurecentered at its seat.

Between the pipe connection 3 and the consumers line 2 a check valve I2is provided, which may be of any type, for example, of the typeillustrated including a iiap valve or closure i3 supported at its upperside ona substantially horizontal pivot pin and closing upon an inclinedseat i5. The system toward which this invention is directed assumes thatthe check valve l2 is not totally effective in preventing back iiow. Thevalve 4 operates as the regulator valve for delivering water at areduced pressure to the consumers line during normal ilow and atcessation of normal flow. There is thus established a pressurediierential the magnitude of which depends upon the force oi thev spring7. This pressure diierential must be of suicient magnitude to permit theoperation of the drain or relief valves to drain or relieve the systemshould the consumers line pressure approach the supply line pressure ator within the said differential.

The connection 3 may be provided directly with a drain valve, but in thepresent instance:

this is accomplished by employing a T connection i5 from which adownpipe I1 extends, said down-f pipe being provided with a drain valvei8, the

delivery side of which is connected to a pipe I9*v that may lead to adrain or to a waste pipe connection. Within the casing of valve i8 avalve closure or disc 20 is provided that normally rests against a seat2l, andthe stem of this valveclosure 20 is attached to a movable,pressurecontrolled memben such as a diaphragm 22,'

which is clamped up at its edge between the body of the valve I8 and itscover 23.

On the side toward the valve cover a pressure 25 as in Fig. l, which isconnected into a pipe 26 that leads oif from the supply line I adjacentto the inlet side of the valve 4. This pipe 26 includes a section 25athat leads off from the pilot valve 25 into the chamber 24.

This pilot valve 25 is normally maintained in an open position throughthe agency of a pressure-controlled device 27 the casing of which iscomposed of two sections 27a and 2lb. Within this pressure device apressurehcontrolled member such as a diaphragm 28 is provided on oneside of which a pressure chamber 23 is formed which is connected by apipe 3? to the supply line I so that the pressure of the said supplyline is maintained in this chamber. On the other side of the diaphragm28 lies a pressure chamber 3| that is connected by the pipe 32 to' theintermediate connection 3. Under normall conditions this gives adifferential pressure acting on the diaphragm 28, the higher pressurebeing, of course, in the chamber 29. Hence the dia phragm is normallyheld displaced toward the right, as viewed in Fig. 1, and in a positionto hold a rack 33 that is attached to the diaphragm in an extended orextreme position. In this position the teeth of this rack meshing with apinion 34 on the plug 35 of the pilot valve hold this plug with its port36 in a position to maintain communication between the pipe 26 and thepipe 263.

Resilient means 33 is provided for urging the diaphragm 28 toward itsother extreme position in opposition to the pressure within the chamber29. The force exerted bythe resilient means 38 is supplemented by thepressure of the fluid beyond the flow control valve 4 so that shouldthis pressure rise to a point where its force exerted against thediaphragm 28, plus the force exerted by the spring 38, is greater thanthe inflow force from the induction line I into the chamber 29, the rack33 will be moved to a position to drain the line 3 between the checkvalve I2 and flow control valve 4 through the pilot valve 35. v

With the organization of parts described above it will be evident thatthe poppet type valve 4 under normal conditions will maintain adifferential pressure vbetween the supply line I and the consumers line2, the amount of which, of course, will depend upon the strength of thecoil spring 1. As the area of the diaphragm exposed in the two chambers29 rand 3l is substantially the same, the preponderance of pressure inthe chamber 29 will normally hold the diaphragm in the position shown inFig. 1, and in this way the pilot valve 25 is maintained open, andthepressure existing in the` supply line I will also be maintained in thechamber 24, and this pressure is, of course, higher than the pressureexisting in the chamber 24a on the other side of the diaphragm 22. Thisinsures that under normal conditions the valve closure 20 will be heldon its seat 2l. If, however, an abnormal condition arises, involving areduction in the amount of this differential pressure below thepredetermined minimum, the spring 38, aided or not by pressure in thechamber 3I, will move the diaphragm 28 toward the left, therebyoperating the rack 33 to move the valve plug 35 to its drainingposition, in which it will relieve the pressure in the chamber 24,whereupon the valve closure 2D will move away from its seat and permitwater in the intermediate chamber or casing 3 to drain oi.

The construction disclosed in Fig. 2 ls substantially the same as thatdisclosed in Fig. 1, except that the pilot valve 25 and its operatingdevice is omitted, and the drain valve is biased to open by means of aspring directly associated with it. Referring to Fig. 2, Ia indicates apoppet type regulator valve which has the same construction as the valve4 shown in Fig. 1, and |22 indicates a check valve having the sameconstruction as the check valve I2. Between these valves 4a and I2a` apipe connection 3i, like the chamber 3, is provided, to which a downpipe I'Ia is connected, leading to a drain valve 39. The casing of thisdrain valve 39 is divided in two' sections 39a and 39h, bolted togetherso as to enclose a pressure chamber in which pressure controlled meansis mounted for assisting in controlling the drain valve closure 40, thatis normally held on its seat through the agency of the differentialpressure between the supply line Ia ahead of the valve 4a, and thepressure existing in the pipe connection or casing 3B, the pressure ofwhich iscommunicated down to the interior of the casing of the drainvalve directly through the pipe Il, This pipe connects up to a port 4Iwithin the valve casing 39, that communicates with the pressure chamber42 on one side of the diaphragm 43 that is held between the two sections39a and 39h.

The valve closure 4U is providedv with a centering stem 44 which isguided at its outer end in the bonnetsection 39a of the valve casing,and guided at its inner end in a bore 45 formed in the adjacent wall ofthe casing 39; in addition to this, resilient means is provided forbiasing this valve toward its open position. In the present instance,this resilient means is a coil spring 46 housed in a cylindrical springchamber 4l' formed in the valve casing 39', and through which the drainwater ows when the valve is in its open position. The spring chamber 4Topens on its side into a drain pipe 48' leading to a waste pipe, or toany suitable drain.

With the organization of parts illustrated in Fig. 2, it will be evidentthat as long as sufficient diiTerential pressure exists between thepressure in the pressure chamber 49 on the left of the diaphragm and thelow pressure chamber 42 on the right, the diaphragm 43 will be heldover, as illustrated in Fig. 2,V so as to hold the valve closure 4I) onits seat; but if this differential pressure falls below a predeterminedlimit, the spring 46 will operate to open the valve 40 and permit thewater in the connections 3 and I'Ia to drain out through thedi'ainvalve.

Although in Fig. 2 I have illustrated a simple diaphragm for cooperatingwith the spring 46 to control the functioning ofthe drain valve 4I), itshould be understood that any type or pressure controlled deviceoperated by the diere'ntial pressure of the supply line and consumersline could be employed, instead of the diaphragm.

In Fig. 3 I illustrate a construction in which the drain valve iscontrolled through the agency of a Sylphon or bellows cooperating with abiasing spring exerting its force in a direction to open the drain valvewhen the differential pressure falls below a predetermined minimum.

In Fig. 3 the direction of flow is from left to right, as in Figs. 1 and2. The liquid passes from the supply line 5I) to a gate valve 5I, andthence through an elbow connection 52 which is formed at the upper endof a substantially vertical leg 53 that conducts the incoming liquiddown to a check valve 54 that opensk in the direction of flow, beingnormally held on its lower seat 62 by ing this valve 01T its seat 52 andtoward its upper seat 6 i. In Fig. 3'this valve is shown in its closedposition, whichit would have when the apparatus is functioning to closeoi, or isolate, the valve chamber 55 from the supply line 55 andconsumers line 51. rlhis position would be assumed whenever the pressurein the supply line reaches atmospheric, or below. rIhe valve 'chamber 56and its communicating passages form the intermediate chamber between thevalve 64 and a check valve 53 which is interposed in the line of flowand permits liquid to pass thro-ugh to the delivery gate valve 59.

The valve chamber is illustrated as formed integral within a casing 50integral with the leg 53 that leads the water in from the elbow 52.

The Valve 563 operates to form an air gap and move-s to the positionindicated in Fig. 3 only in response to the development of atmosphericor sub-atmospheric pressure within the supply line 5B, under whichconditions the spring 55 acts to move the valve 55 against the seat 5.!and to vent the chamber 53 to the atmosphere, preventing back-siphonageof any fluid into the supply line 55.

The main valve Sil is mounted to seat .against the seat 1! and to closethe passage from the duct 63 under the inuence of a spring 55. rhisvalve is in the form of a spring-loadedvalve which acts to maintain aVdiierential pressure between the pressure within the chamber 55 and thepressure within the duct E3 under normal flow and at the instant ofcessation of flow, between the pressure of the liquid within the chamber55 and within the supply line 55.

It will be apparent therefore that there is a pressure differentialestablished between the pressure in the supply line 55 and in theconsum# ers line 5i, the pressure in the consumers line always beingbelow the pressure in the supply line 55 by this differential duringnormal flow and at the instant of cessation of normal flow.

In order to drain automatically the liquid from the valve chamber 55under abnormal conditions such as when diierential pressure between thesupply line 55 and the consumers line 5l or chamber 55 `talls below apredetermined minimum, provide a drain valve i2 that is normally held onits seat 'i5 around the edge of a drain nication with, and normallycarries the pressure of, the supply line 5G.

To communicate this pressure, I provide a pipe fitting i5 that isattached to the outer end of the Sylphon, and this iitting is connectedto a tubular connection 11 which, in the present instance, is in theform of a goose-neck that leads over from a iitting 18 that is connectedto a port 15 formed through the wall of the elbow 52. The outside ofvthe Sylphon, of course, is exposed to the pressure or liquid'in theintermediate cham ber, or valve chamber 55, which pressure is lower thanthe pressure in the supply line 5o due to the action of the springloadedvalve Eli. The Sylphon 'i5 is secured to the stern 'l22L of thevalve 12 so that the pressure within the Sylphon acts in a direction tomove the drain valve 12 against the seat'13. The action of the pressureinside the Sylphon is opposed by spring 8|] and the presf.

sure outside the Sylphon spring 8i) is of such. strength that undernormal operation the pres-V sure differential between pipe 5E) andchamber 55 is sufcient to maintain the drain valve 12 closed. However,if the pressure in chamber 58 approaches the pressure in pipe 55 withinthe limits or` the pressure differential, relief valve 12 will start toopen and drain the fluid from chamber 55. The foregoing arrangementassures that the drain valve 12 will not open to drain the chamber 5Suntil the main valve es has closed and contrariwise insures that thedrain valve 12 will close before the main valve 54 has opened on returnof normal flow through the system.

The underside of the valve 12 is provided with guide wings 8l thatcenter this valve with respect to the outlet 1t as the valve movedtowards or away from its seat.

The connections between the delivery side of the casing B0 and the checkvalve 58 may include a coupling 82 in between thimbles or nipples 83 and54 that connect up to the parts on each side of the coupling. Q

The operation of the embodiment of my invention illustrated in Figure 3is: During normal owing of fluid from the supply line 55 to theconsumers line 51, the vacuum breaker Valve 5f! is seated uponv its seat52. The main valve 55 is open, compressing the spring 69. The drainvalve 12 is closed, compressing the spring 85 and of course the checkvalve 58 is open as are valves 5I and 55. During normal flow thepressure within the chamber 55 and also within the consumers line 51is'lower than the pressure within the supply line 5i). The spring 69 maybe of such force as to maintain a suitable pressure diierential. Themagnitude of this diierential will remain the same irrespective of thepressure fluctuations within the supply line 5i! so that say there was100 lbs. pressure in the supply line 55, and the spring 59 exerted aforce sufficient to reduce the pressure 20 lbs., the pressure Within thechamber 55 would be 80 lbs. and would be less than lbs. in the consumersline 51. As the full pressure of lbs. is exerted through the bellows 15against the spring 85, the drain valve 12 would b maintained tightlyclosed. At the instant of cessation of iiow, the pressure in the chamber56 would build up to 80 lbs., at which time the main valve 54 wouldclose and remain closed.

Under this condition, the drain valve 12 would also remain closed andthe vacuum breaker valve 54 would remain upon its seat 52. If acondition existed in the consumers line 51 which would otherwise resultin a condition of backflow as by the pressure in the consumers linebuilding up or rising to a point where the pressure in the chamber 55was greater than 80 lbs., and

assuming that this occurred during a condition of normal ow, the mainvalve 54 would first close and as the pressure built up to overcome theforce of the pressure exerted within the bellows 15this pressure` wouldact on the outside of the bellows in conjunction with the spring 80 toopen the drain valve and drain the chamber 55, maintaining thiscondition of drain until the pressure in the consumers line again fellbelow the pressure differential, at which time the drain valve 12 wouldclose. If, on the other hand,'the condition of back-siphonage developedin the supply line 55 which would reduce the supply line pressurev sothat the diierence in the pressure within the supply line 59 and withinthe con- 75 sumers line 51 was less than the Yassumed dif;-v

ferential of lbs. the same action would take place, that is, of firstclosing the main valve 64 and then opening the relief valve 'I2 to drainthe chamber 56. If the pressure in the supply line 56 fell toatmospheric pressure or below dueto the development of a partial vacuumin the supply line 56, the vacuum breaker Valve 54 would move from itsposition in engagement with the seat 62 to the position of engagementwith the seat 6i, thereby opening the chamber 63 t0 the atmosphere. Whenthe pressure again built up Within the supply line 50 so that backlowwould not occur, the vacuum breaker valve 54 would again move to itsclosed position within the seat 62 and the pressure would build upwithin the chamber 63 and in the bellows 'i5 until the main valve 64opened. The opening of the main valve 64 would, however, not occur untilthe drain valve 12 had closed due to the difference in eiective forcesexerted by the springs 69 and 80.

It will be observed that if for any reason a leak developed in thebellows "i5, that this leakage would occur into the chamber 55 with theresult that the pressure within this chamber 56 was built up causing thedrain valve l2 to open under the influence of the spring 80 draining thechamber 56. However, as this pressure builds up within the chamber 55,the main valve 64 would close. As the drain valve 12 continues to leak,it would give evidence immediately oi the fact that the bellows hadruptured. The same result would follow from a leaking main valve 64.

Many other embodiments of this invention may be resorted to withoutdeparting from the spirit of the invention.

I claim:

1. In a backlow prevention device for pre-- venting back siphoning orback flow in a pipe system through which a liquid flows from a source toa consumers line, the combination of a chamber member positioned in thepipe system, a flow control valve within the chamber member, springmeans for spring loading the control valve to a closed position, thecontrol valve being mounted in the chamber member to open in thedirection of normal iiow therethrough, a drain valve for draining thechamber, said spring means being adapted to exert a predetermined forceto move the flow control valve to its closed position whereby a definitedrop in pressure is established within the chamber device during normalilow and at the instant ci cessation of flow, pressure actuated meansfor opening and closing the drain valve, and additional means responsiveto the pressure diierential across the ow control valve adapted toenergize the said pressure actuated means. Y

2. In apparatus for preventing backflow, or siphoning from a consumersline back to a supply line, the combination of a duct between saidlines, having a drain outlet with a drain-valve for closing the same;apressure-controlled device having means for opposing to each other thepressure existing in the supply line and the pressure in the consumersline, pressure operated means for actuating the drain valve including apilot valve controlled by said pressure controlled device, meansincluding a spring for biasing the drain-valve toward an open position;a poppettype pressure-regulator valve having a valve-seat and avalve-closure cooperating therewith and opening toward the consumersline, for maintaining a regulated pressure in the consumers line lowerthan that in the supply line; resilient means for urging thevalve-closure to its `closed position and cooperating with the internalpressure of the liquid on the faces of said closure to determine theposition of said closure with relation to said seat; and a check-valvebetween the drain-valve and the consumers line; all of said partscooperating to drain the duct by opening the drain valve and closing thepoppet type valve when the pressure within the duct approaches thepressure in the supply line Within the pressure drop determined by theresilient means biasing the poppet type valve.

3. Means for preventing siphoning or ,backiiow in a pipe system, inwhich liquid ows from a supply source to a consumers line, thecombination of a duct between the supply source and the consumers line,a check-valve between the duct and the consumers line opening in thedirection of normal flow toward the consumers line, a check and flowcontrol valve between the said supply source and said duct, adrain-valve having open and closed positions and connected with saidduct between the said check-valves, including a closure, a pressurechamber with a pressure-controlled member connected with the saidclosure, a pilot valve operable in one position to vent said pressurechamber to atmosphere and operable in another position to admit liquidunder pressure to said pressure chamber for normally holding thedrain-valve closed, a second pressure chamber with itspressure-controlled member connected to said pilot valve, a connectionto said second-named pressure chamber from the supply source on one sideof its pressure-controlled member, a connection to the other side of thesame in said second-named pressure chamber from said duct, and a springassociated with said second-named pressurecontrolled member for urgingthe pilot valve toward its position for venting the iirst-named pressurechamber when the degree of pressure in said duct approaches the degreeof pressure in said supply source.

4. In a backflow prevention device for preventing back-siphoning orbackflow in a pipe system through which a liquid flows from a source toa point of use, the combination `of a chamber member in the pipe system,a flow control valve operatively connected with the chamber member,spring means normally biasing the control valve to a closed position toprovide a predetermined pressure drop in the chamber member, the controlvalve opening in the direction of flow through the chamber member, adrain` valve for draining the chamber member, a pilot member operativelyconnected with the drain valve including fluid pressure actuating meansoperable when the pressure within the cham-ber member approachespressure in the pipe system ahead of the chamber member within thepressure drop for actuating the drain valve to open position to drainliquid from the chamber member.

5. Means for preventing siphoning or backlow in a pipe system in whichow of liquid is normally maintained from a supply source to a consumersline, including a duct between the supply source and the consumers line,a check valve between the duct and the consumers line opening in thedirection of normal flow toward the consumers line; a ow control valvebetween the said supply source and said duct, said ow control valvehaving a valve seat and a springloaded valve closure mounted to moveaway from said seat in the said direction of normal ilow; a

' drain-valve for draining said duct; means including the pilot valvefor operating the drain valve; a differential pressure-controlled meanssubjected to the pressure of the liquid in the duct and the pressure ofsaid supply source, for normally maintaining said pilot valve in oneposition during normal flow, and thereby maintain the drain valveclosed, a spring exerting its force in a direction to effect the openingof the drainvalve; all of said parts cooperating to drain the duct byopening the drain valve and closing said flow control valve when thepressure within the duct approaches the :pressure in the supply sourcewithin the pressure drop determined by the flow control valve.

6. Means for preventing siphoning or backflow in a pipe system, in whichliquid flows from a supply source to a consumers line, the combinationof a duct between the supply source and the consumers line, acheck-valve between the duct and the consumers line opening in thedirection of normal flow toward the consumers line, a ow control valvebetween the said supply source and said duct, spring means biasing theflow control valve to closed position to maintain a predeterminedpressure drop in the liquid passing said iiow control valve, adrain-valve connected with said duct between the flow control valve andsaid check-valve, including a closure element, a pressure chamber with apressurecontrolled member connected with the said closure element, apressure supply means for normally supplying liquid under pressure tosaid pressure-chamber for holding the drain-valve closed, and automaticmeans brought into operation through the agency of the difference ofpressure of the liquid supply upstream from said ow control valve anddownstream from said flow control valve when the said difference inpressure is less than the pressure difference established by thepressure drop determined by the spring biasing means for the flowcontrol valve adapted to cut off said communication and to relieve saidpressure-controlled member so as to permit the drain-valve to open anddrain said duct.

7. A back flow prevention device for use in a fluid distribution systemhaving an induction line and an eduction line connected by anintermediate chamber through which fluid ows under pressure, incombination with means for producing under normal ow and at cessation ofnormal flow a substantial pressure drop between the induction and theeduction lines, a drain valve for draining the intermediate chamber, apilot valve connected with and adapted in one position to effect closingof the drain valve, pressure responsive means adapted to actuate thepilot valve,

said means including a movable element subjected to one side to theinduction pressure and on the other side to the eduction pressure,resilient means biasing the movable element in a direction to shift thepilot valve to another position whereby opening the drain valve ispermitted, said resilient means beingnormally overcome by the normalpreponderance of pressure of the induction line over the eduction line,the resilient means being effective to open the drain valve in the eventthat the degree of said preponderance of induction line pressure shouldbe reduced below a predetermined value.

8. A back ilow prevention device for use in a Iiuid distribution systemhaving an induction LEO line and an eduction line connected by anintermediate chamber through which uid flows under pressure, incombination with means for producing under normal flow and at cessationof normal flow a substantial pressure drop between the induction and theeduction lines, a drain valve for draining the intermediate chamber, apilot valve connectedwith and controlling the opening and closing of thedrain valve, pressure responsive means including a movable elementadapted to actuate the pilot valve, resilient means biasing the movableelement in a direction to open the drain valve, the movable elementbeing urged in the same direction by a lirst force proportional totheeduction pressure and urged in the other direction by a second forceproportional to the induction pressure, said resilient means beingnormally overcome by the normal preponderance of pressure of theinduction line over the eduction line, the resilient means beingeffective to open the drain valve in the event that the degree of saidpreponderence of induction line pressure should be reduced below apredetermined value.

9. Means for preventing siphoning or backiiow in a pipe system, in whichliquid fiows from a supply source to a consumers line, the combinationof a duct between the supply source and the consumers line, acheck-valve between the duct and the consumers line opening in thedirection of normal flow toward the consumers line, a check valve andnow control valve between the said supply source and said duct, `adrainvalve connected with said duct between the said check valve and theflow control valve, including a closure, a pressure chamber with apressurecontrolled member operatively connected to actuate the saidclosure, means for admitting liquid under pressure to said pressurechamber on one side of said pressure-controlled member so that thepressure on said pressure-controlled member urges the closure of saiddrain-valve toward its closed position, said means including a pilotvalve and means responsive to the pressure differential across said iiowcontrol valve for actuating the pilot valve, means for admitting liquidunder pressure from said duct to the other side of saidpressure-controlled member so that the differential between saidpressures on said pressure-controlled member holds the valveclosure inits closed position, and a spring opposing the differential pressure forurging the valve closure to its open position, all of said partscooperating when the degree of pressure in the duct approaches thepressure in the supply source, to actuate said pressure-controlledmember to open said drain-valve.

LEONARD L. SNYDER.

REFERENCES CITED The following references are of record in the rile ofthis patent:

UNITED STATES PATENTS Number Name Date 1,105,991 Miller Aug. 4, 19141,274,680 Calvert Aug. 6, 1918 1,627,628 Anderson May 10, 1927 1,960,144Entriken May 22, 1934 2,146,204 Dore Feb. 7, 1939 2,310,586 Lohman Feb.9, 1943 2,328,118 Ahlport Aug. 31, 1943

